The ultrasonic transducer is utilized as an ultrasonic transmitting-receiving unit for ultrasonic diagnostic apparatus. Recently, the ultrasonic transducer sometimes is attached to a catheter and ultrasonic diagnostic procedure is performed under such condition that the catheter is placed in a human body. In consideration of burden applied to the body, the ultrasonic transducer attached to the catheter should be miniaturized. The miniaturization of the ultrasonic transducer is also required in the case that the probe element is inserted into vascular tracts or narrow body cavities.
Generally, the ultrasonic transducer comprises a thin piezoelectric ceramic sheet piece having a smooth surface on upper and lower sides and a pair of electrode layers each of which is placed on each of the upper and lower side surfaces. On a surface of one electrode layer on which ultrasonic wave is transmitted and received is placed an acoustic matching layer which serves to increase wave-transmission efficiency. On a surface of another electrode layer is placed an acoustic absorbing layer which serves to absorb noise of ultrasonic wave. Generally, both of the acoustic matching layer and acoustic absorbing layer are made of non-electroconductive polymer material. For the known ultrasonic transducer having the above-mentioned structure, it is not easy to connect the upper and lower electrode layers to an outer electric source.
In order to facilitate the connection of the electrode layers to an outer electric source, there has been proposed to extend one of the electrode layers to the side of another (i.e., opposite) electrode layer so that the connections of both electrode layers to an outer electric source can be made on one surface side of the probe element. Generally, an electrode layer extended to the side of the opposite electrode layer is called “turn-up electrode” or “turn-down electrode”.
Japanese Patent Provisional Publication (JPA) 8-280095 discloses an ultrasonic transducer having a turn-down electrode layer which is extended to the bottom surface of the piezoelectric ceramic sheet piece along the side face of the ceramic sheet piece.
Japanese Patent Provisional Publication (JPA) 2001-292495 discloses an ultrasonic transducer having a turn-up electrode layer which is extended to an opposite surface of the piezoelectric ceramic sheet piece along the side faces of the ceramic sheet piece.
As is described above, the use of the turn-up electrode layer or turn-down electrode layer is advantageous for facilitating connection of electrode layers of an ultrasonic transducer to lead wires. However, it is not easy to form the turn-up electrode or turn-down electrode on a highly miniaturized ultrasonic transducer. For example, it is now required to provide such a highly miniaturized ultrasonic transducer as having a size of 1 mm or less which is required for mounting the probe element to a catheter for vascular tracts. However, it is not easy to form the turn-up electrode or turn-down electrode on the highly miniaturized ultrasonic transducer in industrially applicable processes.